Workers cleaning the clock face of Big Ben in London, England (© Reuters)

The National Museum of the American Indian in Washington, DC (© Cvandyke/Shutterstock)

Bison at Yellowstone National Park, Wyoming (© Danny Green/Minden Pictures)

Stepping stones in Tollymore Forest Park, County Down, Northern Ireland (© Chris Curry/500px)

Camels gather with their herders at the Pushkar Camel Fair, Rajasthan state, India (© Anand Purohit/Getty Images)

Saffron crocus flowers in Spain (© Juan-Carlos Munoz/Minden Pictures)

Jardin des Tuileries in autumn, leading to the Louvre Museum in Paris, France (© Brian A. Jackson/Getty Images Plus)

Chapel St-Michel d'Aiguilhe, Le Puy-en-Velay, France (© Jaubert French Collection/Alamy Stock Photo)

The Brandenburg Gate seen through a heart-shaped replica of a remnant of the Berlin Wall (© Britta Pedersen/picture alliance via Getty Images)

Jim Henson, along with Ernie and Bert, rehearses for an episode of 'Sesame Street' in 1970 in New York City (© David Attie/Getty Images)

Vietnam War veteran Jake Thorn (seated) talks to visitors in Aurora, Illinois, in 2013 (© Jeff Haynes/Reuters)

Baby hedgehog (© lorenzo104/Getty Images)

Rodrigo Koxa riding the biggest wave ever surfed, on Nov 8, 2017, off the coast of Nazaré, Portugal (© Pedro Cruz/AP Photo)

The 'Crown of Light' installation is projected onto Durham Cathedral during the 2013 Lumiere Durham festival in England (© Stuart Forster/Alamy)

Starlings at sunset in Blackpool, England (© Mediaworld Images/Alamy)

Fog shrouds the Bavarian Alps in Germany (© Anton Petrus/Getty Images)

For the 30th anniversary of the Velvet Revolution, bridges over the Vltava River, Prague, Czech Republic (© Markus Lange/Offset)

Manatees in the Ichetucknee River in Florida (© Jennifer Adler/Alamy)

Fall colors in Zion National Park, Utah (© pabradyphoto/Getty Images)

Gelada monkeys in Simien Mountains National Park, northern Ethiopia (© Marco Gaiotti/plainpicture)

Lantignié in the Beaujolais region of France (© Jon Arnold/Danita Delimont)

The Cutty Sark in Greenwich, London, England, for its 150th anniversary (© Grant Rooney Premium/Alamy)

For Fibonacci Day, an agave plant (© Moab Republic/Shutterstock)

A bald cypress in the Atchafalaya Basin, Louisiana (© Chris Moore/Tandem Stills + Motion)

Monarch butterflies wintering in Michoacán, Mexico (© Sylvain Cordier/Getty Images)

Highland cattle in Drenthe province in the Netherlands (© defotoberg/Shutterstock)

Aerial view of Sky Harbor International Airport in Phoenix, Arizona (© Nearmap/Getty Images)

｢マルーン・ベルズ｣米国コロラド州, アスペン (© Christopher E. Herbert/Getty Images)

The Maroon Bells, near Aspen, Colorado (© Christopher E. Herbert/Getty Images)

Jemaa el-Fnaa Square in Marrakesh, Morocco (© Pavliha/Getty Images)